Seat belt pretensioner

ABSTRACT

A pretensioner for a seat belt utilizes a relatively inexpensive gas-producing cartridge that is easily replaced after activation so as to condition the pretensioner for subsequent use. The cartridge is similar to a shotgun shell and is chambered in a breech block. The cartridge contains a gas-producing pyrotechnic and a piston. Upon ignition, gas produced by the pyrotechnic effects advancement of the piston which, through an associated mechanism, takes up slack in the seat belt.

BACKGROUND OF THE INVENTION

The present invention relates to seat belt pretensioners and, morespecifically, to a seat belt pretensioner that utilizes a replaceablepyrotechnic cartridge.

Seat belt pretensioners remove slack from a seat belt in the event of acollision in order to minimize forward movement of the passenger. Whileit is known to use pyrotechnic gas generators to operate mechanismswhich wind up or otherwise pull in slack in the seat belt during acollision, such known pyrotechnic gas generators are generally disposedinternally of a seat belt retractor. Thus, the vehicle owner is facedwith a significant cost penalty in that the entire pretensioner andretractor assembly must be replaced after activation because of theinability to conveniently reload the propellant charge and becausehigh-temperature gases tend to abrade interior metal surfaces andproduce ash and clinkers which bind up the retraction mechanism.

Another problem with known pretensioners is that they are designed toactivate only in severe accidents, for example, accidents that exhibit"G" forces sufficient to activate the vehicle airbags. Safety systemdesigners generally choose such a relatively high activation thresholddue to the expense of replacing the entire seat belt retractor andpretensioner assembly after activation. As a result, seat beltpretensioners do not protect passengers in less severe accidents.

A related problem with known pretensioners is that when the pretensioneris activated only in severe accidents, activation is relatively late inthe crash sequence. Thus, the pretensioner must rapidly take up slack inthe seat belt, sometimes injuring the passenger.

SUMMARY OF THE INVENTION

The aforesaid problems are solved, in accordance with a preferredconstructed embodiment of the present invention, by a seat beltpretensioner that utilizes a relatively inexpensive gas-producingcartridge that is easily replaced after activation so as to conditionthe pretensioner for subsequent use.

The replaceable cartridge is similar to a shotgun shell. In thepreferred embodiment of the invention, the cartridge comprises a metalcasing having a gas-producing pyrotechnic and a piston with a rackattached. The replaceable cartridge is chambered in a breech block. Uponignition, gas produced by the pyrotechnic drives the piston and rackaxially of the cartridge. The rack is meshed with a pinion gear whichrotates a standard seat belt retraction mechanism so as to retract thebelt.

After use, only the cartridge, including the piston and rack, need bereplaced, obviating the expense of replacing other components of theseat belt retraction mechanism.

Because expense heretofore associated with activation of a pretensioneris significantly reduced, passengers can be given the protection of seatbelt pretensioning in even minor accidents. Moreover, a pretensionerwhich activates in minor collisions will also activate earlier in asevere crash sequence. Earlier activation of the pretensioner permitsthe pretensioner to operate less aggressively, reducing the possibilityof injury caused by the seat belt pretensioner itself.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagrammatic elevational view, partially in cross-section,of a replaceable seat belt pretensioner cartridge chambered in a breechblock with the rack thereof in engagement with the pinion gear of a beltretraction mechanism;

FIG. 2 is a view taken along the line 2--2 of FIG. 1;

FIG. 3 is a view taken in the direction of the arrow "3" of FIG. 1;

FIG. 4 is a view, similar to FIG. 1, of an alternate embodiment of thepretensioner cartridge showing the piston thereof connected to a pulley;

FIG. 5 is a diagrammatic view of the pretensioner of FIG. 4 showingorientation of the pulley relative to the seat belt retractor mechanism;

FIG. 6 shows an alternate embodiment of the cartridge piston, rack andpinion; and

FIG. 7 shows an alternate mounting system for the pretensioner.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIGS. 1-3, a pretensioner 10 in accordance with a preferredembodiment of the invention, comprises a replaceable cartridge 12adapted to pretension a seat belt 13 of a conventional seat beltretractor 14. A typical seat belt retractor to which the pretensioner ofthe present invention has application, is taught in U.S. Pat. No.4,558,832.

The cartridge 12 comprises a cylinder 16, made from, for example, steel,brass, or aluminum, having a cap 18 closing one end. The cap 18 hasparallel keying surfaces 20 to control orientation of the cartridge 12upon insertion thereof into a complementary breech block 22. When thecartridge 12 is inserted into the breech block 22, the keying surfaces20 align a pair of electrical contacts 24 on the cap 18 withcomplementary contacts 26 on the breech block 22. The contacts 24 on thecartridge 12 lead to a conventional igniter 30 for the ignition of agas-producing pyrotechnic material 32. Ignition of the gas-producingpyrotechnic 32 drives a piston 36 and integral rack 38 to the right, asseen in FIG. 1. A pressure relief vent 40 is provided at the end of thecylinder 16 to vent excess gas pressure to atmosphere after the rack 38on the piston 36 has been fully advanced.

The rack 38 engages a pinion gear 45 on the seat belt retractor 14 toeffect retraction of the belt 13. A guide block 46 maintains the rack 38in engagement with the pinion gear 42.

As seen in FIG. 7 a mounting bracket 41 formed of two hemisphericalsections 42 and 44 surround cylinder 16. The bracket 41 serves the dualfunction of holding the cartridge 12 in place and of providing radialcontainment to the cylinder 16, thus avoiding any tendency of thecylinder 16 to bloat or burst during firing. Proper design of thebracket 41 allows the cylinder 16 to be fabricated from plastic, on theorder of a shotgun shell.

After activation of the pretensioner 10, only the cartridge 12,including the piston 36 and rack 38, need be removed from the breechblock 22 thereof and a new cartridge 12 installed to recondition thesystem.

FIGS. 4 and 5 illustrate an alternate embodiment of the invention whichcould be conveniently packaged in the B-pillar of a vehicle. Apretensioner 50 comprises a cartridge 51 having a piston 52 disposedtherein. The piston 52 is provided with a pulley 54 at the end thereof.A seat belt 56 is routed from a seat belt retractor 58 around the pulley54. When the cartridge 50 is activated, as by an energization of anigniter 60 and ignition of a propellant 62, slack in the seat belt 56 istaken up and the belt 56 is pretensioned. A conventional, normallylocked anti-payout mechanism of the seat belt retractor 58 preventsunreeling of the seat belt 56 when load is placed on the seat belt 56and ensures that all of the travel of the pulley 54 is used to take upslack in the seat belt 56.

As seen in FIG. 6, an alternate embodiment of the invention provides fora programmed decrease in the slack take-up rate thereby to avoid injuryto a vehicle occupant. A piston 70 has a rack 72 that is rampedupwardly, as seen in the drawing, so as to complement a pinion gear 74of increasing diameter. Advancement of the piston 70 and rack 72 effectsprogressively slower rotation of and increased torque on the pinion gear74. A rack with the opposite slope ramp could also be applied to reversethe rotation speed and torque profile, if desired.

While the preferred embodiment of the invention has been disclosed, itshould be appreciated that the invention is susceptible of modificationwithout departing from the scope of the following claims.

I claim:
 1. A pretensioner for a seat belt comprising:a breech block, areplaceable cartridge in said breech block comprising:a cylinder havinga closed end and an open end; a piston in said cylinder; a rack attachedto said piston; and a pyrotechnic in said cylinder between the closedend thereof and said piston for driving said piston and rack relative tosaid cylinder toward the open end thereof; and means connecting saidpiston to said seat belt for taking up slack therein upon ignition ofsaid pyrotechnic and advancement of said piston comprising:a pinion gearreleasably engageable with said rack; and a retraction mechanism for theseat belt driven by said pinion gear.
 2. The seat belt pretensioner ofclaim 1 wherein said pinion gear is of varying diameter so as to varythe rate of rotation thereof in relation to advancement of said piston 9and rack.
 3. A pretensioner for a seat belt comprising:a breech block; areplaceable cartridge in said breech block comprising:a cylinder havinga closed end and an open end; a piston in said cylinder; a pyrotechnicin said cylinder between the closed end thereof and said piston fordriving said piston relative to said cylinder toward the open endthereof; and means connecting said piston to said seat belt for takingup slack therein upon ignition of said pyrotechnic and advancement ofsaid piston comprising a pulley connected to said piston and disposed incontact with the seat belt whereby advancement of said piston and saidpulley tensions said belt.